A general description of the thermodynamic and aerodynamic theory underlying the design of the gas turbine engine is presented by H. Cohen, et. al., Gas Turbine Theory, Second Edition, John Wiley & Sons, 1973. On page 232, the reference discusses "cooled turbines" which involves the application of substantial quantity of coolant to the nozzle and rotor blades. This permits an increase in the turbine inlet temperature and thereby increasing the specific power output. The reference mentions that apart from the use of spray cooling for thrust boosting in turbojet engines, the liquid systems have not proved to be practical. A discussion of some of the materials and processes used in the General Electric heavy duty gas turbines is presented in a paper by F. D. Lordi, Gas Turbine Materials and Coatings, GER-2182J, General Electric Co., 1976. This paper gives a detailed description of the processing techniques for casting turbine buckets and nozzles, the alloys from which they are made, and the application of corrosion resistant coatings.
Structural arrangements for the open-circuit liquid cooling of gas turbine buckets are shown by Kydd, U.S. Pat. No. 3,445,481 and 3,446,482. The first patent discloses a bucket having cooling passages open at both ends which are defined by a series of ribs forming part of the core portion of the bucket and a sheet metal skin covering the core and welded to the ribs. The second patent discloses squirting liquid under pressure into hollow forged or cast turbine buckets. Another patent issued to Kydd, U.S. Pat. No. 3,619,076 describes an open circuit cooling system wherein a turbine blade construction consists of a central airfoil-shaped spar which is clad with a sheet of metal having a very high thermal conductivity, e.g. copper. The cladding sheet has grooves recessed in the sheet face adjacent to the spar, which grooves together with the smooth surface of the spar define coolant passages distributed over the surface of the turbine blade. There are numerous disadvantages in forming liquid cooling passages by bonding a sheet to a core in either of the configurations shown in U.S. Pat. Nos. 3,445,481 or 3,619,076. Thus, when a braze is used to bond the skin, some channels of the turbine buckets become plugged and obstructed with braze material. Excellant bonds are required between the core and the skin to contain the water in full channel flow under the extremely high hydraulic pressures which result from the centrifugal forces during operation of the turbine. In addition, any cracks in the skin can cause leakage of the coolant and result in vane failure.